The present invention relates to general printing field, in particular, offset printing, and a novel offset printing method in which a printing plate can be easily formed, and an offset printing plate. Specifically the present invention relates to an offset printing method capable of replication reclamation of a printing plate precursor and a printing plate precursor.
The offset printing method has been generally used and has become a primary printing means at present because a manufacturing process of a printing plate is simple among various printing methods. This printing technique is based on the incompatibility of oil and water. An oily material, i.e., ink, is retained in an image area and a fountain solution is retained in a non-image area selectively. By bringing an ink carrying-printing plate into contact with a part to be printed directly or indirectly via an intermediate which is called blanket, the ink on the image area is transferred to the part to be printed, thereby printing is performed.
The offset printing method mainly comprises a PS plate comprising an aluminum substrate as a support having coated thereon a diazo photosensitive layer. The aluminum support of a PS plate is surface-grained and anodized to heighten the ink receptivity of the image area and ink repellency of the non-image area through other various processes to thereby improve the press life and contrive accuracy of the printing plate. Accordingly, the offset printing is provided with press life and high accuracy of the printing plate in addition to simplicity.
However, further simplification of the offset printing technique has been required with the prevalence of printed matters and a variety of simple printing methods have been proposed.
Representative examples thereof are copy rapid offset printing plate commercially available from Agfa-Gevaert Co. and a printing method based on printing plate making by means of a silver salt diffusion transfer process as disclosed in U.S. Pat. No. 3,511,656 and JP-A-7-56351 (the term xe2x80x9cJP-Axe2x80x9d as used herein means an xe2x80x9cunexamined published Japanese patent applicationxe2x80x9d). This method has been put to practical use as a simple printing method because a lipophilic transfer image can be formed through one step according to this method, hence the image can be used as a printing plate as it is. However, this method also includes diffusion transfer development process with an alkaline developing solution, although it is simple. Therefore, a further simpler printing method which necessitates no development process with a developing solution has been demanded.
From the above background, a simpler printing plate-making method without performing development with an alkaline developing solution after image exposure has been developed. This simpler printing plate is called a non-processing printing plate because a development process is excluded and many improved methods have been proposed. Every sort and kind of means based on various principles, e.g., (1) image formation by thermal destruction of the irradiated part on image recording surface by imagewise exposure, (2) image formation by lipophilization (heat mode hardening) of the irradiated part by imagewise exposure, (3) image formation by lipophilization (light mode hardening) of the irradiated part by imagewise exposure, (4) decomposition of surface property by photolysis of a diazo compound, and (5) heat transfer of the image area by heat mode melting have been suggested.
The above simple offset printing techniques are disclosed in U.S. Pat. Nos. 3,506,779, 3,549,733, 3,574,657, 3,739,033, 3,832,948, 3,945,318, 3,962,513, 3,964,389, 4,034,183, 4,081,572, 4,693,958, 731,317, 5,238,778, 5,353,705, 5,385,092, 5,395,729 and European Patent 1068.
These techniques do not require a developing solution at plate-making but they have at least one of the drawbacks that the difference between a hydrophilic area and a lipophilic area is insufficient, consequently the image quality of the printed image is inferior, that the resolving power is inferior, consequently a printed image plane having excellent sharpness can hardly be obtained, that the image surface is insufficient in mechanical strength and is liable to be damaged, resulting in the necessity of the provision of a protective film, consequently the simplicity is rather lost, and that the durability capable of enduring long term printing is insufficient. These facts show that only the exclusion of an alkali developing process does not lead to the solution of the problem. Thus, a method for making a printing plate which fulfills requisite characteristics for printing and can easily produce a printing plate has been strongly demanded but such a method has not been realized yet.
On the other hand, along with the simplification of a printing method represented by a non-processing printing plate, reclaiming of used printing plate precursors for recycling is advantageous to the reduction of the costs and wastes and to environmental protection. However, the reclamation and reuse of printing plate precursors are accompanied by various difficulties hence these have been hardly given serious consideration, and only a special material for a printing precursor which is called zirconia ceramic is disclosed in JP-A-9-169098. Zirconia ceramic is, however, insufficient in light sensitivity and light conversion effect from hydrophobicity to hydrophilicity is unsatisfactory, therefore discrimination of an image area from a non-image area is insufficient.
In the above circumstances, the present inventors have proposed a printing plate precursor composed of a thin layer of specific metallic oxides belonging to group II, IV, or V of the Periodic Table, e.g., titanium oxide, and a printing method using the same in JP-A-11-78272, JP-A-11-105234 and Japanese Patent Application Nos. 9-258784, 9-308822, 9-308823, 9-313740, 9-348077, and 9-348078. This is a non-processing printing plate precursor which can be easily reclaimed and is excellent in simplicity, economization and environmental suitability but the present inventors have found that this printing plate precursor is inferior in ink stain of the printed paper when repeatedly used in comparison with the printed paper obtained by using a new printing plate precursor. Therefore, it has been desired to develop a method which generates little ink stain with repeated use of the printing plate precursor and which can maintain the printing quality of the printed paper in the initial printing.
This printing plate precursor has a thin layer the surface of which becomes hydrophilic with the irradiation of active light and becomes lipophilic by absorbing light energy, and the above-described simplicity and environmental suitability of this printing plate precursor are satisfied due to this constitution. However, it is desired to further increase the sensitivity to active light and the sensitiveness of the transformation of the physical properties of the thin layer surface by heat energy absorption to heighten the ink-receptivity and ink-repellency of the printing plate precursor to thereby improve the printing quality of the printed paper.
Accordingly, an object of the present invention is to improve the above-described non-processing printing plate precursor having a thin layer composed of a specific metallic oxide, specifically an object is to provide a printing plate precursor having high sensitivity to active light, having high sensitiveness of the transformation of the physical properties of the surface by heat energy absorption, hence hydrophilicity and lipophilicity are highly discriminable, and excellent in ink-receptivity and ink-repellency.
Another object of the present invention is to improve the above-described non-processing printing plate precursor having a thin layer composed of a specific metallic oxide which can be reclaimed repeatedly, specifically another object is to provide an offset printing means which generates little ink stain of the printed paper when the printing plate precursor is reused and can maintain the printing quality of the printed paper even when the printing plate precursor is repeatedly used, consequently to provide an offset printing means capable of increasing the number of times of the capability of repeating use of the printing plate precursor.
The present inventors have searched for a recording method having high heat-response for achieving the above objects. As a result, the present inventors have found that the response sensitivity of the transformation of the surface physical properties due to the action of heat increases by providing, as an auxiliary layer, a radiation ray-absorbing layer just under a photosensitive layer. As a result of further investigation based on this fact, the present invention has been attained.
Moreover, for achieving the above objects, the present inventors have eagerly examined the cause of ink stain, and have elucidated that ink stain was caused by the ink remaining on the used printing plate precursor which could not be completely removed by cleaning. Based on this fact, the present inventors have searched for a means to exclude the ink from the printing plate, thus the present invention has been achieved.
That is, the present invention has been achieved by the following means.
(1) An offset printing plate precursor comprising a substrate having provided thereon a thin layer, wherein printing is performed by following the steps of:
(a) subjecting the printing plate precursor to irradiation with active light,
(b) subjecting the printing plate precursor to irradiation with light/heat convertible radiant rays or heat treatment, to thereby imagewise distribute a hydrophilic area and a lipophilic area of the thin layer, and
(c) bringing the thin layer into contact with printing ink to form a printing plate in which the lipophilic area has received the printing ink, to thereby perform offset printing.
(2) The offset printing plate precursor as described in the above item (1), wherein printing is performed by following the steps of (a) subjecting the printing plate precursor to irradiation with active light, (b) subjecting the printing plate precursor to irradiation with light/heat convertible radiant rays, to thereby imagewise distribute a hydrophilic area and a lipophilic area of the thin layer, and (c) bringing the thin layer into contact with printing ink to form a printing plate in which the lipophilic area has received the printing ink, to thereby perform offset printing,
wherein a layer containing a substance capable of absorbing radiant rays and converting the radiant energy to heat energy is provided between the thin layer and the substrate and in contact with the thin layer.
(3) The offset printing plate precursor as described in the above item (2), wherein the thin layer provided on the substrate is a thin layer composed of at least one compound selected from the group consisting of TiO2, RTiO3 (wherein R represents an alkaline earth metal atom), AB2xe2x88x92xCxD3xe2x88x92xExO10 (wherein A represents a hydrogen atom or an alkali metal atom, B represents an alkaline earth metal atom or a lead atom, C represents a rare earth atom, D represents a metal atom belonging to metal elements of Group V-A of the Periodic Table, E represents a metal atom belonging to metal elements of Group IV of the Periodic Table, and x represents an arbitrary numerical value of from 0 to 2), SnO2, Bi2O3, and Fe2O3.
(4) The offset printing plate precursor as described in the above item (2), wherein the substance capable of absorbing radiant rays and converting the radiant energy to heat energy is a metal or a metal compound accompanied by a self exothermic reaction.
(5) The offset printing plate precursor as described in the above item (2), wherein the printing plate precursor can be restored to the original condition before use and repeatedly used by removing the remaining ink on the printing plate after printing has been finished by cleaning and then heating the surface of the plate precursor at 80xc2x0 C. or higher.
(6) The offset printing plate precursor as described in the above item (1), wherein printing is performed by following the steps of (a) subjecting the printing plate precursor to irradiation with active light, (b) subjecting the printing plate precursor to heat treatment, to thereby imagewise vary the degree of hydrophilicity and lipophilicity of the thin layer, and (c) bringing the thin layer into contact with printing ink to form a printing plate in which the lipophilic area has received the printing ink, to thereby perform offset printing,
wherein the thin layer provided on the substrate is a thin layer composed of at least one compound selected from the group consisting of TiO2, RTiO3 (wherein R represents an alkaline earth metal atom), AB2xe2x88x92xCxD3xe2x88x92xExO10 (wherein A represents a hydrogen atom or an alkali metal atom, B represents an alkaline earth metal atom or a lead atom, C represents a rare earth atom, D represents a metal atom belonging to metal elements of Group V-A of the Periodic Table, E represents a metal atom belonging to metal elements of Group IV of the Periodic Table, and x represents an arbitrary numerical value of from 0 to 2), SnO2, Bi2O3, and Fe2O3, and
the surface of the thin layer is a scabrous surface comprising concavities and convexities having an arithmetic mean pore diameter calculated in terms of a circle of the concavities of at least 1.0 xcexcm.
(7) The offset printing plate precursor as described in the above item (6), wherein printing is performed by following the steps of (a) subjecting the printing plate precursor to irradiation with active light, (b) subjecting the printing plate precursor to heat treatment, to thereby imagewise vary the degree of hydrophilicity and lipophilicity of the thin layer, and (c) bringing the thin layer into contact with printing ink to form a printing plate in which the lipholic area has received the printing ink, to thereby perform offset printing,
wherein the printing plate precursor can be restored to the original condition before use and repeatedly used by removing the remaining ink on the printing plate after printing has been finished by cleaning and then heating the surface of the plate precursor at 80xc2x0 C. or higher.
(8) An offset printing method which comprises:
(a) subjecting a printing plate precursor to irradiation with active light,
(b) subjecting a printing plate precursor to irradiation with light/heat convertible radiant rays or heat treatment, to thereby imagewise distribute a hydrophilic area and a lipophilic area of a thin layer provided on a substrate, and
(c) bringing the thin layer into contact with printing ink to form a printing plate in which the lipophilic area has received the printing ink, to thereby perform offset printing.
(9) The offset printing method as described in the above item (8), which comprises (a) subjecting a printing plate precursor to irradiation with active light, (b) subjecting a printing plate precursor to irradiation with light/heat convertible radiant rays, to thereby imagewise distribute a hydrophilic area and a lipophilic area of the thin layer provided on the surface of the printing plate precursor, and (c) bringing the thin layer into contact with printing ink to form a printing plate in which the lipophilic area has received the printing ink, to thereby perform offset printing,
wherein a layer containing a substance capable of absorbing radiant rays and converting the radiant energy to heat energy is provided between the thin layer and the substrate and in contact with the thin layer.
(10) The offset printing method as described in the above item (9), wherein the thin layer is a thin layer composed of at least one compound selected from the group consisting of TiO2, RTiO3 (wherein R represents an alkaline earth metal atom), AB2xe2x88x92xCxD3xe2x88x92xExO10 (wherein A represents a hydrogen atom or an alkali metal atom, B represents an alkaline earth metal atom or a lead atom, C represents a rare earth atom, D represents a metal atom belonging to metal elements of Group V-A of the Periodic Table, E represents a metal atom belonging to metal elements of Group IV of the Periodic Table, and x represents an arbitrary numerical value of from 0 to 2), SnO2, Bi2O3, and Fe2O3.
(11) The offset printing method as described in the above item (9) , wherein the substance capable of absorbing radiant rays and converting the radiant energy to heat energy is a metal or a metal compound accompanied by a self exothermic reaction.
(12) The offset printing method as described in the above item (9), wherein the printing plate precursor can be restored to the original condition before use and repeatedly used by removing the remaining ink on the printing plate after printing has been finished by cleaning and then heating the surface of the plate precursor at 80xc2x0 C. or higher.
(13) The offset printing method as described in the above item (9), which comprises the steps of:
(a) subjecting all over the surface of the thin layer on the surface of the printing plate precursor to irradiation with active light to make all over the surface of the thin layer hydrophilic,
(b) subjecting the surface of the thin layer to imagewise irradiation with light/heat convertible radiant rays to make the irradiated part lipophilic, and
(c) bringing the surface of the thin layer into contact with printing ink to form a printing plate in which the lipophilic area has received the printing ink, to thereby perform offset printing.
(14) The offset printing method as described in the above item (9) , wherein the printing plate precursor is repeatedly used by following the steps of:
(a) subjecting all over the surface of the thin layer on the surface of the printing plate precursor to irradiation with active light to make all over the surface of the thin layer hydrophilic,
(b) subjecting the surface of the thin layer to imagewise irradiation with light/heat convertible radiant rays to make the irradiated part lipophilic,
(c) bringing the surface of the thin layer into contact with printing ink to form a printing plate in which the lipophilic area has received the printing ink, to thereby perform offset printing,
(d) removing the remaining ink on the surface of the thin layer after printing has been finished by cleaning, and
(e) heating the surface of the thin layer at 80xc2x0 C. or higher, thereby all over the surface of the thin layer is restored to its lipophilic condition.
It is also the characteristic of the offset printing material of the present invention to repeatedly use the printing plate precursor by utilizing the reversible variable property of hydrophilicity and lipophilicity of the printing plate precursor as follows.
(15) The offset printing method as described in the above item (9) , wherein the printing plate precursor is repeatedly used by following the steps of:
(a) imagewise distributing a hydrophilic area and a lipophilic area on the thin layer provided on the surface of the printing plate precursor,
(b) bringing the thin layer into contact with printing ink to form a printing plate in which the lipophilic area has received the printing ink, to thereby perform offset printing,
(c) removing the remaining ink on the printing plate after printing has been finished by cleaning, and
(d) heating the surface of the plate precursor at 80xc2x0 C. or higher, thereby the printing plate precursor can be restored to the original condition before use.
(16) The offset printing method as described in the above item (9), wherein the printing plate precursor is repeatedly used by following the steps of:
(a) subjecting all over the surface of the thin layer provided on the surface of the printing plate precursor to irradiation with active light to make all over the surface of the thin layer hydrophilic,
(b) subjecting the surface of the thin layer to imagewise irradiation with light/heat convertible radiant rays to make the irradiated part lipophilic,
(c) bringing the surface of the thin layer into contact with printing ink to form a printing plate in which the lipophilic area has received the printing ink, to thereby perform offset printing,
(d) removing the remaining ink on the printing plate after printing has been finished by cleaning, and
(e) heating the surface of the plate precursor at 80xc2x0 C. or higher, thereby the printing plate precursor can be restored to the original condition before use.
(17) The offset printing method as described in the above item (8), wherein the printing plate precursor is repeatedly used by following the steps of:
(a) subjecting the printing plate precursor to irradiation with active light,
(b) subjecting the printing plate precursor to heat treatment, to thereby imagewise distribute a hydrophilic area and a lipophilic area of the thin layer,
(c) bringing the thin layer into contact with printing ink to form a printing plate in which the lipophilic area has received the printing ink, to thereby perform offset printing
(d) removing the remaining ink on the printing plate after printing has been finished by cleaning, and
(e) heating the surface of the plate precursor at 80xc2x0 C. or higher, thereby the plate precursor is restored to the original condition before use and repeatedly used.
(18) The offset printing method as described in the above item (17), wherein the printing plate precursor is repeatedly used by following the steps of:
(a) subjecting all over the surface of the thin layer on the surface of the printing plate precursor to irradiation with active light to make all over the surface of the thin layer hydrophilic,
(b) subjecting the surface of the thin layer to imagewise heating to make the irradiated part lipophilic,
(c) bringing the surface of the thin layer into contact with printing ink to form a printing plate in which the lipophilic area has received the printing ink, to thereby perform offset printing,
(d) removing the remaining ink on the surface of the thin layer after printing has been finished by cleaning, and
(e) heating the surface of the thin layer at 80xc2x0 C. or higher, thereby all over the surface of the thin layer is restored to its lipophilic condition.
(19) The offset printing method as described in the above item (17), wherein the printing plate precursor is repeatedly used by following the steps of:
(a) subjecting the surface of the thin layer on the surface of the printing plate precursor to imagewise irradiation with active light to make the irradiated part of the thin layer hydrophilic,
(b) bringing the surface of the thin layer into contact with printing ink to form a printing plate in which the lipophilic area has received the printing ink, to thereby perform offset printing,
(c) removing the remaining ink on the surface of the thin layer after printing has been finished by cleaning, and
(d) heating the surface of the thin layer at 80xc2x0 C. or higher, thereby all over the surface of the thin layer is restored to its lipophilic condition.
(20) The offset printing method as described in the above item (8), wherein the active light for use in imagewise irradiation is laser beam.
The present invention is the improved invention based on the non-processing printing plate precursor having a thin layer composed of a substance which becomes hydrophilic by the irradiation with active light, in particular a thin layer composed of the above-described specific metallic oxide, and the printing method using the same as the fundamental techniques, and the object has been achieved by the existence of a substance capable of absorbing radiant rays and converting the radiant energy to heat energy for further improving the heat energy-response.
The fundamental invention is a method for producing a non-processing printing plate for offset printing and a printing plate precursor for use in the method, which has been attained on the basis of the characteristic physical properties of a thin layer composed of a specific metallic oxide, i.e., imagewise distribution of a hydrophilic area and a lipophilic area was formed by making use of the properties of the metallic oxide that (1) the surface of the thin layer is converted to hydrophilic by the irradiation with active light, and (2) the surface of the thin layer is converted to lipophilic by heating, and this thin layer was employed as the ink-receiving area and the ink-repelling area. Further, the fundamental invention also involves a method for reclaiming used printing plate precursors for recycling by utilizing the foregoing characteristics of conversion by heating of the surface physical properties of the thin layer. As described above, the foregoing fundamental techniques are disclosed in by JP-A-11-28272, etc.
As compared with the fundamental invention, the present improved invention is an invention of a printing method and a printing plate precursor which comprises a layer containing a substance having a function capable of absorbing light/heat convertible radiant rays and converting the radiant energy to heat energy (hereinafter referred to as xe2x80x9clight/heat conversion) provided just under the image-recording layer. The present invention aims at improving image-forming sensitivity and ink-receptivity concurrently.
Accordingly, the constitution of the offset printing plate precursor according to the present invention comprises a substrate having provided thereon a layer containing a light/heat convertible substance, and thereon a thin layer which becomes hydrophilic with the irradiation of active light and becomes lipophilic by the function of light/heat convertible radiant rays, in particular a specific metallic oxide described later.
Another characteristic of the fundamental invention is that a printing plate precursor can be restored to the original condition before use and repeatedly used by removing the remaining ink on the printing plate after printing has been finished by cleaning and then heating the surface of the plate precursor at 80xc2x0 C. or higher, and the present invention has succeeded to this characteristic.
Further, the present invention has been improved in reducing stain due to printing by using, as fundamental techniques, the non-processing printing plate precursor having the above-described specific metallic oxide thin layer on a printing plate surface and the printing method using the same.
The fundamental technique is to use a printing plate precursor, wherein the thin layer provided on the substrate is a thin layer composed of at least one compound selected from the group consisting of TiO2, RTiO3 (wherein R represents an alkaline earth metal atom), AB2xe2x88x92xCxD3xe2x88x92xExO10 (wherein A represents a hydrogen atom or an alkali metal atom, B represents an alkaline earth metal atom or a lead atom, C represents a rare earth atom, D represents a metal atom belonging to elements of Group V-A of the Periodic Table, E represents a metal atom belonging to elements of Group IV of the Periodic Table, and x represents an arbitrary numerical value of from 0 to 2), SnO2, Bi2O3, and Fe2O3, and the degree of hydrophilicity and lipophilicity of the thin layer is imagewise varied by irradiation with active light and heat treatment, then the thin layer is brought into contact with printing ink to form a printing plate in which the lipophilic area has received the printing ink, and the remaining ink on the printing plate after printing has been finished is removed by cleaning and the surface of the plate precursor is then heated at 80xc2x0 C. or higher, thereby the printing plate precursor which can be repeatedly used can be restored to the original condition before use.
That is, a thin layer composed of a specific metallic oxide is characterized in that the surface property thereof becomes hydrophilic by irradiation with active light and the converted surface property is restored to the original hydrophobic property by heating. A non-processing printing plate precursor for offset printing is produced by applying these two characteristics to the discrimination of ink-receptivity from ink repellency, and used printing plate precursors are reclaimed for recycling also by utilizing the above heat conversion characteristics of the surface physical properties.
As described above, the foregoing fundamental techniques are disclosed in JP-A-11-78272.
The improved point of the present invention based on the above fundamental technique is that the surface of the thin layer on the substrate is a scabrous surface comprising concavities and convexities having an arithmetic mean pore diameter calculated in terms of a circle of the concavities of at least 1.0 xcexcm.
The cardinal point of the present invention is to exclude minute structure of surface unevenness as has been made clear that the remaining ink is insistently adhered onto the minute part of surface uneven structure of a printing plate and does not dissolve in a detergent when a used printing plate precursor is washed with an ink detergent. Surface roughness is necessary for increasing the retaining property of a fountain solution of the ink-repellent part on a printing plate during printing, but it is not necessary to be especially minute and it should be sufficient that concavity and convexity have a large period in some degree.
Degree of minuteness of uneven structure can be expressed by a mean pore diameter calculated in terms of a circle by taking the arithmetic mean value of the diameter of one concavity (referred to as xe2x80x9cequivalent circle pore diameterxe2x80x9d) regarding the concavity as a circular concavity. The object of the present invention has been attained by employing a printing plate precursor in which the surface of the thin layer has mean equivalent circle pore diameter of at least 1 xcexcm. Degree of minuteness of the unevenness of a printing plate is adjusted by adjusting the unevenness of the surface of the printing plate substrate. As the thin layer is exceedingly thin, the unevenness of a substrate is directly reflected.